How much computing power does it cost to run GPT-3?
I can't anwser your question on how much computing power you might need, but you'll need atleast a smallgrid to run the biggest model just looking at the memory requirments (175B parameters so 700GB of memory). The biggest gpu has 48 GB of vram  I've read that gtp-3 will come in eigth sizes, 125M to 175B parameters. So depending upon which one you run you'll need more or less computing power and memory. (https://lambdalabs.com/blog/demystifying-gpt-3/) 
For an idea of the size of the smallest, &quot;The smallest GPT-3 model is roughly the size of BERT-Base and RoBERTa-Base.&quot;